Our long-range goal is to understand how the neural mechanisms for pursuit and saccadic eye movements operate in health and in various human disease states and how these motor mechanisms are related to visual perception and cognition. Although pursuit and saccades have long been viewed as distinct motor systems, there is growing evidence that certain crucial steps are shared. This overlap likely ensures that pursuit and saccades work together during normal visually guided behavior. The objective of this application is to investigate the nature and degree of this functional overlap. In particular, we will examine how the superior colliculus participates in the selection of targets for pursuit and saccades. Our primary hypothesis is that the selection of targets for pursuit and saccades is guided by common neural signals that are read out in parallel by the two motor systems. The project will address the following four questions: (1) Can neuronal activity in the superior colliculus account for the behaviorally observed tradeoffs between speed and accuracy for pursuit and saccades? (2) Do pursuit and saccades select targets in parallel or is selection by the pursuit system serially linked to that by the saccade system? (3) Is activity throughout the superior colliculus selective for the location of pursuit targets, or is this property restricted to the rostral portion? (4) What are the relative contributions of the superior colliculus and the frontal eye fields to target selection for pursuit and saccades? At the completion of this research, we expect to understand how activity in the superior colliculus is related to the mechanisms of target selection for pursuit and saccades, and to have determined the extent to which pathways through the superior colliculus and the frontal eye fields are crucial for the normal control of pursuit eye. These studies are a step toward understanding how the brain coordinates the components of voluntary movements and how it establishes and regulates the link between visual processing and movement selection. The results from these studies will therefore help refine clinical descriptions of the oculomotor system that are used to diagnose eye movement disorders in humans.